You need to ground the Ground plate to the chassis, right there by mean of a bolt and a clear surface (sand paint back to make a good contact and cover area with spark lug sealant to prevent rusting. The negative of the battery in the trunk you ground out in the trunk.
As for the positive terminal, you need to run your positive cable from the trunk to the front where the battery was originally, and hook it up to the original positive wire through an insulated distribution block.
